code: def __len__(self):
      return len(self.data_index)
  
file_path: PGL/examples/gnn_depoly/node_classification_with_sampling/dataset.py
imports: import numpy
  import paddle
  from paddle.io import Dataset, DataLoader
  from pgl.sampling import graphsage_sample
label_desc: Use image node_id 3 for calling the ShardedDataset obj's underlying member method code with example usage: obj.__len__() and returns: len